Nanoparticles with antimicrobial properties are used in thousands of nano-enabled consumer products. Therefore, it is important to understand the response mechanisms of bacteria that are exposed to these nanoparticles at different conditions. Moreover, it is necessary to evaluate possible microbial adaptation mechanisms. In our study, Escherichia coli K-12 MG1655 (E. coli) were grown continuously in bioreactors at two specific growth rates (0.1 h⁻¹ and 0.2 h⁻¹) and then exposed to chronic concentrations of casein-coated silver nanoparticles (AgNPs) [1 mg L⁻¹] for about 180 generations. After initiating the injection of AgNPs, the results showed a change in growth kinetic parameters between non-exposed and exposed systems. Maximum yield (Y_max) decreased by 33%, while the maintenance coefficient (m_s) increased by 52%. This evidence was indicating the versatility of the culture to growth in the exposed conditions and even the ability to achieve a new stationary state. However, the adaptation was achieved at a metabolic cost. Comparing the concentration and composition of extra-cellular substances that were produced showed differences between the control and exposed conditions, and also between the exposed systems in the two growth conditions. In the AgNPs-exposed bioreactor (EB) growing at 0.1 h⁻¹, AgNPs–ES complexes showed that the ratio of the area representing β-sheets to the area representing α-helix proteins was 2.4, which implies the formation of a protein corona, while at an exposed growth rate of 0.2 h⁻¹ this ratio was <1, indicating no protein corona. Transcriptomic results showed gene regulation in response to AgNPs exposure as a function of the specific growth rate. Batch exposure tests using the resultant cultures for each condition showed a lower inhibitory effect for the AgNPs on EB at 0.1 h⁻¹ than on control bacteria (CB) at 0.1 h⁻¹ in terms of membrane permeation and reactive oxygen species generation. Overall, our study showed that culture growth conditions significantly affects bacterial response to nanoparticle exposure. Therefore, these growth parameters should be determined and reported when performing toxicological tests.

Ceramic water filters (CWFs) are point-of-use drinking water treatment systems that are manufactured and used in under-served communities around the world. The clayey material (CM) used to manufacture CWFs is a locally sourced mixture of clay, sand, slit and amorphous material (usually dug near the CWF factory). CM varies in composition and purity depending on the geographical location and geological setting. In this study, a set of 13 CM samples collected from around the world were analyzed using grain size analysis, as well as liquid and plastic limit tests. Mineralogical composition was determined using X-ray diffraction. A selection of three CM samples (Guatemala, Canada, and Guinea Bissau) with a range of compositions were used to study biofilm growth on CM before and after firing. Biofilm coverage was studied on CM (before firing) and CWF material (after firing) using Pseudomonas fluorescens Migula. The average biofilm coverages for Guatemala, Canada, and Guinea Bissau CM were 20.03 ± 2.80%, 19.28 ± 0.91%, and 9.88 ± 4.02%, respectively. The average biofilm formation coverages for Guatemala, Canada, and Guinea Bissau CWF were 13.08 ± 1.74%, 10.36 ± 3.41%, and 8.66 ± 0.13%, respectively. The results presented here suggest that CM can be manipulated to manufacture better performing CWFs by engineering the soil characteristics, such as grain size, liquid and plastic limits, and mineralogy. This could improve the durability and biofilm resistance of CWFs.

Ensuring access to safe drinking water remains a crucial global challenge, particularly in low-income and developing regions. Point-of-use (POU) sand filters, known for their affordability and efficiency, hold promise for improving water quality. This study explores the use of copper mesh (M-Cu) as a disinfectant in sand filters, focusing on its effectiveness against Escherichia coli (E. coli). Through a series of experiments—kinetic, batch, and column—we investigated the impact of M-Cu on bacterial inactivation. Our findings reveal that the contact time between the M-Cu and bacteria is more critical than the M-Cu mass for achieving significant microbial reduction. Specifically, 1.0 g of M-Cu can substantially reduce E. coli levels, achieving log removal values (LRVs) between 2.03 and 4.81 after 30 min of exposure, across initial bacterial concentrations ranging from 10² to 10⁶ CFU/100 mL. For sand filter testing under dynamic conditions, columns containing 1.0 g of M-Cu achieved a 3.1 LRV, significantly outperforming control columns, which only achieved a 0.6 LRV. These results support the integration of M-Cu into sand filters as a viable strategy for enhancing microbial safety in water treatment, potentially reducing waterborne disease incidence in vulnerable populations.

The scope of discussion of this Special Issue includes, but is not limited to, understanding the fate, transport, removal, and modeling of traditional and emerging pollutants in water